Concrete pipe development

October 4, 2016

Innovations in pipe manufacture and seal design maximize performance.

By Julian West

As the trend toward urbanization continues unabated, so too does the need to provide underground infrastructure to meet the sanitation needs of so-called mega cities. Similarly, as the world’s population increases, the need to connect ever more remote places and lay pipeline in more extreme environments also grows.

This can present challenges, both in terms of material performance and durability of pipeline infrastructure, as well as installation. Ensuring that the jointing of concrete pipelines is given full and proper consideration will have a significant impact on the long-term service of the pipeline itself.

Overview of pipe developments

Concrete pipes have been used for water and wastewater applications for many decades; in fact their origins can be traced back to Roman times. The manufacturing process has developed significantly, but design of the joint has perhaps seen the biggest changes.

Originally, pipes were made using centrifugal spinning techniques, where a cylindrical mold was spun on rollers and the concrete fed inside. The centrifugal forces distributed the concrete around the inside of the mold to form the pipe.

The big change came when vertical casting was introduced. This system uses an outer mold with an inner core and semi-dry concrete is fed round the annulus between the two. Vibration is applied to get the desired level of compaction. Using this method, the pipe can be molded immediately and mold equipment can be recycled for the next pipe. Naturally, this makes the process much faster and more cost effective.

Until the 1960s, most water and sewer pipe joints were rigid and made from horse hair, tarred rope, and cement mortar. Then, flexible rubber joints were introduced to allow for the natural movement between pipes without causing damage. This technology has been developing ever since.

Now, the ability to integrate flexible rubber seals within a concrete pipe socket during manufacture is raising standards of leak tightness from infiltration and exfiltration, ease and reliability of jointing, and long-term seal durability. Similarly, it is reducing margin for error, including incorrect or missing seals, poor installation, and push-back.

Partnership in pipe design

There is now an abundance of application-specific seals which, if used correctly, can continuously optimize pipe infrastructure performance. Pipe manufacturers who fully utilize the partnership with their seal manufacturer will gain from the expertise and valuable technical advice and support they have to offer. This should include training on how to use the seals — specifically how to joint them and how they function — as well as a strong knowledge of water infrastructure requirements across the globe, including relevant legislation.

A seal manufacturer should provide the necessary expertise to design-in features that can overcome issues, for example, optimizing jointing forces at low temperatures to create zero push-back during installation. An expert understanding of rubber’s behavior is imperative if the seal is to perform exactly as required over its life.

The type of rubber used for pipe seals should be comprehensively considered, as the right choice will aid in extending the life of the asset and infrastructure as a whole. Seals are primarily available in two types of rubber — styrene-butadiene rubber (SBR) and ethylene propylene diene monomer rubber (EPDM). The former has traditionally always been used in pipe seal manufacturing, but in some cases EPDM can offer additional benefits. It is ozone resistant, offers long-term stress relaxation performance (maintaining its elastic properties for longer), and ensures optimized rubber stability and durability. EPDM is ideal for integrated systems.

Challenges of production and installation

Production of an integrated seal within a concrete pipe must be carefully managed, otherwise challenges can arise, including incorrect positioning of the seal on the pallet, concrete ingress between the seal and pallet, and compression or displacement of the seal during concrete compaction.

Once the seal is in place within the pipe, it cannot easily be moved or replaced, making it vital that the seal performs as required, first time, to avoid unnecessary lost time and money associated with pipe scrappage.

This is where seal design is so imperative. A seal that is manufactured using co-extrusion methods will ensure high performance. Specifically, slurry lips made of soft rubber — 50 International Rubber Hardness Degrees (IRHD) — will provide improved flexibility, and an enhanced seal profile will ensure a more secure fit against the pallet, removing risk of leaking concrete and unnecessary pallet cleaning. To increase stability and grip, the forming parts of the seal should be made from harder material, such as 70 IRHD rubber.

The combination of soft and hard rubbers means that the seal has optimum stiffness so the profile doesn’t compress, the right level of stability for reduced risk of seal displacement, and superior flexibility for the optimum sealing capabilities. In all, a seal with these properties guarantees extended asset and infrastructure life as well as reduced scrap rates.

The industry is being driven forward through innovations such as co-extrusion manufacturing technology and automatic pipe laying. This reduces the need for people in the trench during installation, lessening the potential for human error and offering health and safety benefits. Innovation in the form of improved materials, products, and installation techniques is vital in order to continuously improve efficiency, reduce costs, and maximize the performance and longevity of pipeline infrastructure.